Ethyl(1-p-fluorophenyl-6-fluoro-7-chloro-4-oxo-1,4-dihydro-quinoline-3-carb oxylate) is an intermediate for the preparation of 1-p-fluorophenyl-6-fluoro-1,4-dihydro-4-oxo-7-(4-methyl-1-piperazinyl)-3-q uinoline-carboxylic acid of antibacterial activity (24th Intersci. Conf. Antimicrob. Agents. Chemother. 1984. Abst. 72-78). The latter compound can be prepared from ethyl-(1-p-fluorophenyl-6-fluor-7-chloro-4-oxo-1,4-dihydro-quinoline-3-car boxylate) in two steps. The 1-p-fluorophenyl-6-fluoro-1,4-dihydro-4-oxo-7-(4-methyl-1-piperazinyl)-3-q uinoline-carboxylic acid can be prepared by reacting 1-p-fluorophenyl-6-fluoro-7-chloro-1,4-dihydro-4-oxo-quinoline-3-carboxyli c acid (obtained by hydrolyzing the ester) with 1-methyl-piperazine in the presence of a solvent at a temperature of 100.degree. C. for 20 hours (European Patent Specification No. 131839).
The ethyl-(1-cyclopropyl-6-fluoro-7-chloro-4-oxo-1,4-dihydro-quinoline-3-carbo xylate) is an intermediate for the preparation of 1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinoline-car boxylic acid which has antibacterial activity (Eur. J. Clin. Microbiol. 1983., 2, 111). The latter compound can be obtained from ethyl-(1-cyclopropyl-6-fluoro-7-chloro-4-oxo-1,4-dihydro-quinoline-3-carbo xylate) in two steps. After hydrolyzing the ester, the 1-cyclopropyl-6-fluoro-7-chloro-1,4-dihydro-4-oxo-quinoline-3-carboxylic acid thus obtained is reacted with piperazine in the presence of a solvent at a temperature of 135.degree.-140.degree. C. for two hours and thus 1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7(1-piperazinyl)-quinoline-3-carb oxylic acid can be prepared (German Off. No. 30 33 157 and No. 31 42 854).
The 1-substituted-6,7,8-trifluoro-4-oxo-1,4-dihydro-quinoline-3-carboxylic acid derivatives (GB patent No. 2057440, Belgian patent specification 887574, European patent No. 106489 and No. 15049, German patent No. 3433924, Japanese patent Nos. 60006684 and 61085381, Portugal patent No. 80187) are intermediates for the preparation of 7-substituted-6,8-difluoro-1,4-dihydro-4-oxo-quinoline-3-carboxylic acid derivatives (J. Med. Chem. 1986. 29, 445; Drugs Fut. 1984. 9, 246; 23rd Intersci. Conf. Antimicrob. Agents Chemother. 1983. Abstr. 658; 7th Int. Symp. Fut. Trends Chemother. 1986, 80).